Waved filter media and elements

ABSTRACT

Various high performance, high efficiency filter media are provided that are cost effective and easy to manufacture. In particular, various filter media are provided having at least one layer with a waved configuration that results in an increased surface area, thereby enhancing various properties of the filter media. The filter media can be used to form a variety of filter elements for use in various applications.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/509,571, filed Oct. 8, 2014, which is a continuation of U.S.patent application Ser. No. 13/565,524, filed on Aug. 2, 2012, which isa continuation of U.S. patent application Ser. No. 12/508,770, filed onJul. 24, 2009, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/399,281, filed on Mar. 6, 2009, which is acontinuation-in-part of U.S. patent application Ser. No. 12/038,049,filed on Feb. 27, 2008, which claims priority to U.S. ProvisionalApplication No. 60/986,626 filed on Nov. 9, 2007 and U.S. ProvisionalApplication No. 60/892,025 filed on Feb. 28, 2007, which are all herebyincorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to filtration, and more particularly tohigh capacity filter media and elements.

BACKGROUND OF THE INVENTION

The removal of air borne particulate contaminants from the air is aconcern to everyone. Gas phase particulate filtration has traditionallybeen accomplished by methods that utilize woven or nonwoven fabrics orwebs. The performance of such a system is characterized by the initialefficiency of removal or capture of the particulate as a function ofparticle size, the initial resistance of the system to air or gas flowas a function of gas flow rate or face velocity, and the way both ofthese factors change as the filter element loads with the particulatecontaminant. One common measurement is the alpha value of a media, whichis the product of the pressure drop and the filtration efficiency, andis calculated as follows:

alpha=−100*log((100−efficiency)/100)/Pressure Drop.

Generally, it is desirable that a particular filter media have a higheralpha value, as this is indicative that media has a low pressure dropand a high efficiency. For example, the glass materials that are usedfor ASHRAE bag filters have alpha values (obtained with a DOP challenge)that are in the range of 12-16 (depending upon the particular efficiencyof the media), and are not reliant on any type of electrostatic chargeto achieve this alpha value. Glass paper can have alpha values of about12-13, membrane materials can have alpha values of about 20, andnanofiber electrospun materials can have alpha values in the range ofabout 5-12. None of these materials is reliant on any type ofelectrostatic charge to achieve these alpha values.

Filtration media formed from using meltblown, spunbond, carded nonwoven,and wet laid synthetic materials can have very high alpha values whenthey are electrostatically charged. However, when the charge is removed,the alpha values of these media significantly decreases to levels thatare well below the alpha values of media made using other materials.

Accordingly, there remains a need to provide an improved filter, andmore particularly to provide filter media and filter elements havingimproved alpha values, including those that can maintain high alphavalues during use.

SUMMARY OF THE INVENTION

In one embodiment, a filter media is provided having a membranefiltration layer and a coarse support layer that holds the membranefiltration layer in a waved configuration and maintains separation ofpeaks and troughs of adjacent waves of the filtration layer.

In one embodiment, a filter media is provided having a fine fiberfiltration layer and a coarse support layer that holds the fine fiberfiltration layer in a waved configuration and maintains separation ofpeaks and troughs of adjacent waves of the filtration layer. The layersof the filter media, as well as the various properties of each layer canvary. In one embodiment, the coarse support layer has a fiber mass thatis less at the peaks than a fiber mass in the troughs. In anotherembodiment, the fine fiber filtration layer can have a surface area thatis at least 50%, and more preferably 100%, greater than a surface areaof the fine fiber filtration layer in a planar configuration. In anotherembodiment, the coarse support layer can be a downstream coarse supportlayer, and the filter media can further include an upstream coarsesupport layer. The fine fiber filtration layer can be disposed betweenthe upstream coarse support layer and the downstream coarse supportlayer. The filter media can also include at least one additionalfiltration layer disposed between the downstream coarse support layerand the upstream coarse support layer. In one exemplary embodiment, theat least one additional filtration layer can be formed from fibershaving an average diameter greater than an average fiber diameter offibers that form the fine fiber filtration layer.

The fiber diameters of the various layers can vary. In one embodiment,the upstream coarse support layer can be formed from fibers having anaverage diameter greater than an average diameter of fibers forming thefine fiber filtration layer and equal to or less than an averagediameter of fibers forming the downstream coarse support layer. In anexemplary embodiment, the upstream coarse support layer, the fine fiberfiltration layer, and the downstream coarse support layer all have awaved configuration. In some cases, one or more of the upstream coarsesupport layer, the fine fiber filtration layer, and the downstreamcoarse support layer are charged. In an exemplary embodiment, the filtermedia has about 2 to 6 waves per inch. The upstream and downstreamcoarse support layers can be formed from, for example, staple fiberlayers, and the fine fiber filtration layer can be at least one of ameltblown layer and a glass fiber layer. The coarse support layer canalso be formed from at least one binder fiber and at least onenon-binder fiber.

In another embodiment, the filter media can include at least one of aplanar layer disposed upstream of the upstream coarse support layer anda planar layer disposed downstream of the downstream coarse supportlayer. The planar layer can be formed from fibers having an averagediameter less than an average diameter of fibers forming the upstreamcoarse support layer and the downstream coarse support layer, andgreater than an average diameter of fibers forming the fine fiberfiltration layer. In another embodiment, the planar layer can be formedfrom fibers having an average diameter that is greater than the upstreamand downstream coarse support layers and the fine fiber filtrationlayer. In such an embodiment, the planar layer is preferably disposeddownstream of the downstream coarse support layer.

The filter media can also have various properties. For example, thefilter media can have a DOP alpha value of greater than about 9, andmore preferably greater than about 11; a dust holding capacity of atleast about 8 g/ft² at 25 FPM face velocity using ASHRAE dust loading to1.5 inch H₂O pressure drop; a NaCl loading of less than about 50 mm H₂Oafter loading approximately 60 mg/100 cm² of 0.26 μm particles at 25 FPMface velocity; an air permeability in the range of about 10 CFM to 300CFM; a basis weight in the range of about 70 gsm to 1100 gsm; and/or athickness in the range of about 1.5 mm to 25 mm.

In yet another embodiment, a filter media is provided having a firstfibrous layer with a waved configuration forming a plurality of waves,each wave having a random wave form and height, and each wave having apeak and a trough, adjacent peaks being spaced a distance apart from oneanother and adjacent troughs being spaced a distance apart from oneanother. The filter media can also include a second fibrous layer matedto the first fibrous layer and formed from fibers that are more coarsethan fibers forming the first layer.

In one embodiment, the first fibrous layer can have a surface area thatis at least about 50% greater, and more preferably 100% greater, than asurface area of the first fibrous layer in a planar configuration. Thefirst fibrous layer can be formed from, for example, fine fibers havingan average diameter less than an average diameter of fibers forming thesecond fibrous layer. The average diameter of the fibers of the firstfibrous layer can be less than about 5 μm and the average diameter ofthe fibers of the second fibrous layer is greater than about 10. Inanother embodiment, the second fibrous layer can have a fiber densitythat is greater adjacent to the peaks of the first fibrous layer thanthe fiber density adjacent to the troughs of the first fibrous layer.The second fibrous layer can be disposed downstream of the first fibrouslayer, and the filter media can also include a third fibrous layerdisposed upstream of the first fibrous layer. In one exemplaryembodiment, the third fibrous layer is formed from fibers having anaverage diameter that is equal to or less than an average diameter offibers forming the second fibrous layer, and the diameter of the fibersforming the second fibrous layer is greater than an average diameter offibers forming the first fibrous layer. The first, second, and thirdfibrous layers can have a waved configuration, and the filter media canalso include at least one of a fourth layer disposed upstream of thethird fibrous layer and having a planar configuration and a fifth layerdisposed downstream of the second fibrous layer and having a planarconfiguration. In certain exemplary embodiments, the first fibrous layeris a meltblown layer or a glass fiber layer, and the second fibrouslayer is formed from at least one binder fiber and at least onenon-binder fiber.

In yet another embodiment, a multi-layer filter media is provided havinga curvilinear web formed from a fine fiber layer and at least one coarsesupport layer formed from a blend of binder fibers and non-binderfibers. The at least one coarse support layer can maintain spacingbetween adjacent peaks of the fine fiber layer and maintain spacingbetween adjacent troughs of the fine fiber layer. The filter media canalso include a planar web mated to the curvilinear web.

In one embodiment, the fine fiber layer can be a meltblown layer or aglass layer, and the at least one coarse support layer can be formedfrom at least one binder fiber and at least one non-binder fiber. The atleast one coarse support layer can include a first coarse support layerdisposed upstream of the fine fiber layer and a second coarse supportlayer disposed downstream of the fine fiber layer. The planar web can bedisposed upstream of the first coarse support layer. In an exemplaryembodiment, the second coarse support layer is formed from fibers havingan average fiber diameter that is greater than an average fiber diameterof fibers forming the first coarse support layer, and the average fiberdiameter of the fibers forming the second coarse support layer isgreater than an average fiber diameter of the fibers forming planar web,and the average fiber diameter of the fibers forming the planar web isgreater than an average fiber diameter of fibers forming the fine fiberlayer. In other aspects, the fine fiber layer can have a surface areathat is at least about 50% greater than a surface area of the fine fiberlayer in a planar configuration.

In other aspects, a filter element is provided having a filter mediawith at least two fibrous layers having a waved configuration such thatthe filter media includes a plurality of non-uniform waves having aheight that is about 2″ or less. At least one of the fibrous layers canbe a fine fiber filtration layer, such as a meltblown layer or a glasslayer, and at least one of the fibrous layers can be a coarse fibersupport layer. The filter element can also include a housing disposedaround a perimeter of the filter media. In one embodiment, the housingcan be formed by stiffening a portion of the perimeter of the filtermedia. In another embodiment, the housing can be a frame disposed aroundthe perimeter of the filter media. The filter media preferably has aMERV rating of 7 to 16.

In another embodiment, a pleated filter element is provided having afiltration layer and a support layer mated together to form a wavedfilter media with a plurality of peaks and troughs. The waved filtermedia is pleated. In an exemplary embodiment, the waved filter mediaincludes a stiff backing sufficient to allow the waved filter media tomaintain pleats. Alternatively or in addition, the waved filter mediacan have a stiffness that allows the waved filter media to maintainpleats. In an exemplary embodiment, the waved filter media has athickness, before pleating, of about 0.5″ or less, and a thickness whenpleated of about 12″ or less, and more preferably about 2″ or less. Thepleated waved filter media can also include a housing disposed around aperimeter of the filter media. In an exemplary embodiment, the pleatedfilter media has MERV rating of 7 to 16.

In other aspects, a bag filter is provided having a housing and aplurality of filters mated to the housing. Each filter can have a pocketformed therein and can be configured to receive airflow therethrough,and each filter can be formed from a filter media having a first fibrouslayer, such as a meltblown or glass layer, that is held in a wavedconfiguration by a second fibrous layer to form peaks and troughs. Thehousing can be, for example, a frame and an open end of each filter canbe mated to the frame. The filters can be positioned parallel to oneanother. The filters can also optionally include at least one spacerdisposed therein and adapted to maintain opposed sidewalls of the filterat a predetermined distance apart from one another. In an exemplaryembodiment, the filter media has a thickness that is about 2″ or less,and more preferably about 0.5″ or less, and/or a MERV rating in therange of about 7 to 16, and more preferably about 10 to 16. The filtermedia can also include a third fibrous layer disposed on a side of thefirst fibrous layer opposite to the second fibrous layer.

In one set of embodiments, a filter media includes a fine fiberfiltration layer comprising a plurality of waves having peaks andtroughs in a waved configuration, and a coarse support layer that holdsthe fine fiber filtration layer in the waved configuration and maintainsseparation of peaks and troughs of adjacent waves of the filtrationlayer. In one embodiment, the filter media has an initial DOP alphavalue of greater than about 40. In another embodiment, the filter mediahas a DOP alpha value of greater than about 9 at 60 minutes. In yetanother embodiment, the filter media has a pressure drop from NaClloading of less than 30 mm H₂O at 60 minutes. The fine fiber filtrationlayer in some such embodiments may be electrostatically charged, and mayinclude, for example, fibers having an average diameter of about 5 μm orless, e.g., about 1.5 μm or less. Furthermore, the filter media may havean initial pressure drop of less than about 10.0 mm H₂O, or less thanabout 3.0 mm H₂O. For certain applications, the filter media has aninitial DOP penetration of less than about 90% and a penetration at 60minutes of DOP loading of less than about 95%, or an initial DOPpenetration of less than about 30% and a penetration at 60 minutes ofDOP loading of less than about 65%. The amplitude of the peaks andtroughs may be between about 0.1″ and about 4.0″, between about 0.1″ andabout 1.0″, or between about 0.1″ and about 0.3″. The frequency of themedia can also vary. For example, the filter media may have 2 to 6 wavesper inch, e.g., about 3 waves per inch. The filter media can be used ina variety of applications including, for example, facemasks andrespirators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view illustration of one embodiment of a filter media;

FIG. 1B is a side view illustration of another embodiment of a filtermedia;

FIG. 1C is a side view illustration of one layer of the filter media ofFIG. 1A;

FIG. 2A is a perspective view of one embodiment of a panel filter;

FIG. 2B is a side cross-sectional view of the panel filter of FIG. 2Ataken across line 2B;

FIG. 3 is a side view of another embodiment of a panel filter;

FIG. 4A is a perspective view of one embodiment of a pleated filterelement;

FIG. 4B is a side cross-sectional view of another embodiment of apleated filter element;

FIG. 4C is a side cross-sectional view of yet another embodiment of apleated filter element;

FIG. 5A is a perspective view of one embodiment of a bag filter havingmultiple filter bags disposed therein;

FIG. 5B is a perspective view of one of the filter bags of FIG. 5A;

FIG. 5C is a side cross-sectional view of the filter bag of FIG. 5B;

FIG. 6 is a chart showing discharged DOP penetration versus pressuredrop for various filter media;

FIG. 7 is a chart showing dust holding capacity for various filtermedia;

FIG. 8 is a chart showing NaCl Loading for various filter media;

FIG. 9 is a chart showing a multi-pass liquid test for various filtermedia;

FIG. 10 is a chart showing DOP alpha versus time for various filtermedia;

FIG. 11 is a chart showing pressure drop during DOP loading versus timefor various filter media;

FIG. 12 is a chart showing DOP penetration versus time for variousfilter media;

FIG. 13 is a chart showing NaCl loading versus time for various filtermedia;

FIG. 14 is a chart showing pressure drop during NaCl loading versus timefor various filter media;

FIG. 15 is a chart showing NaCl penetration versus time for variousfilter media; and

FIG. 16 is a chart showing filtration efficiency versus particle sizerange for various filter media.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. Thoseskilled in the art will understand that the devices and methodsspecifically described herein are non-limiting exemplary embodiments andthat the scope of the present invention is defined solely by the claims.The features described in connection with one exemplary embodiment maybe combined with the features of other embodiments. Such modificationsand variations are intended to be included within the scope of thepresent invention.

The present invention generally provides various high performance, highefficiency filter media that are cost effective and easy to manufacture.In particular, various filter media are provided having at least onelayer with a waved configuration that results in an increased surfacearea, thereby enhancing various properties of the filter media. Thefilter media may optionally be charged and can be used to form a varietyof filter elements for use in various applications.

Media

In general, various filter media are provided having at least onefiltration (e.g., fibrous, membrane) layer that is held in a waved orcurvilinear configuration by one or more additional layers (e.g.,fibrous). As a result of the waved configuration, the filter media hasan increased surface area which results in improved filtrationproperties. The filter media can include various layers, and only someor all of the layers can be waved.

FIG. 1A illustrates one exemplary embodiment of a filter media 10 havingat least one filtration layer and at least one coarse support layer thatholds the filtration layer in a waved configuration to maintainseparation of peaks and troughs of adjacent waves of the filtrationlayer. The filtration layer(s) may be charged or uncharged. In theillustrated embodiment, the filter media 10 includes a fine fiberfiltration layer 12, a first, downstream coarse support layer 14, and asecond, upstream coarse support layer 16 disposed on opposite sides ofthe fine fiber filtration layer 12. The support layers 14, 16 can helpmaintain the fine fiber filtration layer 12, and optionally anyadditional filtration layers, in the waved configuration. While twocoarse support layers 14, 16 are shown, the filter media 10 need notinclude both support layers. Where only one coarse support layer isprovided, the coarse support layer can be disposed upstream ordownstream of the filtration layer(s). One or more of the coarse supportlayer(s) may be charged in certain embodiments.

The filter media 10 can also optionally include one or more outer orcover layers located on the upstream-most and/or downstream-most sidesof the filter media 10. FIG. 1A illustrates a top layer 18 disposed onthe upstream side of the filter media 10 to function as an upstream dustholding layer. The top layer 18 can also function as an aesthetic layer,which will be discussed in more detail below. The layers in theillustrated embodiment are arranged so that the top layer 18 is disposedon the air entering side, labeled I, the second coarse support layer 16is just downstream of the top layer 18, the fine fiber filtration layer12 is disposed just downstream of the second coarse support layer 16,and the first coarse support layer 14 is disposed downstream of thefirst layer 12 on the air outflow side, labeled O. The direction of airflow, i.e., from air entering I to air outflow O, is indicated by thearrows marked with reference A.

The outer or cover layer can alternatively or additionally be a bottomlayer disposed on the downstream side of the filter media 10 to functionas a strengthening component that provides structural integrity to thefilter media 10 to help maintain the waved configuration. The outer orcover layer(s) can also function to offer abrasion resistance. FIG. 1Billustrates another embodiment of a filter media 10B that is similar tofilter media 10 of FIG. 1B. In this embodiment, the filter media 10Bdoes not include a top layer, but rather has a fine fiber filtrationlayer 12B, a first coarse support layer 14B disposed just downstream ofthe fine fiber filtration layer 12B, a second coarse support layer 16Bdisposed just upstream of the fine fiber filtration layer 12B on the airentering side I, and a bottom layer 18B disposed just downstream of thefirst coarse support layer 14B on the air exiting side O. Furthermore,as shown in the exemplary embodiments of FIGS. 1A and 1B, the outer orcover layer(s) can have a topography different from the topographies ofthe fine fiber filtration layer and/or any coarse support layers. Forexample, in either a pleated or non-pleated configuration, the outer orcover layer(s) may be non-waved (e.g., substantially planar), whereasthe fine fiber filtration layer and/or any coarse support layers mayhave a waved configuration. A person skilled in the art will appreciatethat a variety of other configurations are possible, and that the filtermedia can include any number of layers in various arrangements.

Fine Fiber Layer

As indicated above, in an exemplary embodiment the filter media 10includes at least one fine fiber filtration layer 12, which mayoptionally be charged. In an exemplary embodiment, a single filtrationlayer 12 formed from fine fibers is used, however the filter media 10can include any number of additional optionally charged filtrationlayers disposed between the downstream coarse support layer and theupstream coarse support layer, adjacent to the fine fiber filtrationlayer 12, or disposed elsewhere within the filter media. While notshown, the additional filtration layer(s) can be maintained in a wavedconfiguration with the fine fiber filtration layer 12. In certainexemplary embodiment the filter media 10 can include one or moreadditional filtration layers disposed upstream of the fine fiberfiltration layer 12. The additional filtration layer(s) can be formedfrom fine fibers, or more preferably can be formed from fibers having anaverage fiber diameter that is greater than an average fiber diameter ofthe fibers that form the fine fiber filtration layer 12.

The fine fiber filtration layer 12 can be formed from a variety offibers, but in an exemplary embodiment the fine fiber filtration layer12 is formed from fibers having an average fiber diameter that is lessthan about 10 μm, and more preferably that is less than about 5 μm, andmore preferably that is less than about 3 μm. In certain exemplaryembodiments, the fibers can have an average fiber diameter of about 1.5μm or less, including nanofibers having an average diameter of less thanabout 1 μm, e.g., about 0.5 μm. In some embodiments, the fibers have anaverage fiber diameter of between about 0.3 μm and about 1.5 μm, orbetween about 0.3 μm and about 1.0 μm.

If provided, any additional filtration layers can likewise be formedfrom a variety of fibers, but in an exemplary embodiment the additionalfiltration layer(s) is/are formed from fibers having an average fiberdiameter that is greater than about 5 μm but preferably that is lessthan about 10 μm.

Various materials can also be used to form the fibers, includingsynthetic and non-synthetic materials. In one exemplary embodiment, thefine fiber filtration layer 12, and any additional filtration layer(s),is formed from meltblown fibers. Exemplary materials include, by way ofnon-limiting example, polyolefins, such as polypropylene andpolyethylene; polyesters, such as polybutylene terephthalate andpolyethylene terephthalate; polyamides, such as Nylon; polycarbonate;polyphenylene sulfide; polystyrene; and polyurethane. In anotherembodiment, the fine fiber filtration layer 12 can be formed from glassfibers. Various manufacturing techniques can be used to form the glassfiber web, include wetlaid or drylaid webs. The type and size of glassfiber can also vary, but in an exemplary embodiment, the fiber is amicroglass fiber, such as A-type or E-type glass fibers made using arotary or flame attenuation process and having an average fiber diameterin the range of about 0.2 μm to 5 μm. However, other suitable materialsinclude, by way of non-limiting example, polyvinyl alcohol andpolyvinylidene fluoride. The fine fiber filtration layer 12, and anyadditional filtration layer(s), can also be formed using various othertechniques known in the art, including wet laid techniques, air laidtechniques, carding, electrospinning, and spunbonding. In embodiments inwhich the fine fiber filtration layer is charged, the layer may becharged prior to joining with another layer, or after a composite of twoor more layers has been formed.

The resulting fine fiber filtration layer 12, as well as any additionalfiltration layer(s), can also have a variety of thicknesses, airpermeabilities, basis weights, and filtration efficiencies dependingupon the requirements of a desired application. In one exemplaryembodiment, the fine fiber filtration layer 12, as measured in a planarconfiguration, has a thickness in the range of about 0.1 mils to 30mils; for example, between about 0.1 mils to 2 mils, or between about 2mils to 12 mils. The fine fiber filtration layer may have an airpermeability in the range of about 10 CFM to 1000 CFM. For example, thepermeability may be between about 10 CFM to 300 CFM, or between about600 CFM to 700 CFM. The basis weight may be in the range of about 0.1gsm to 50 gsm, for example, between about 5 gsm to 40 gsm. The DOPfiltration efficiency of the fine fiber filtration layer may vary widelydepending on the particular application, but is generally in the rangeof about 20% to 99.999%. For example, for certain applications, the fineDOP efficiency may be between about 95 to 99.999%. If any additionalfiltration layers are provided, in certain exemplary embodiments eachadditional filtration layer, as measured in a planar configuration, hasa thickness in the range of about 0.1 mils to 30 mils, an airpermeability in the range of about 10 CFM to 1000 CFM, a basis weight inthe range of about 0.1 gsm to 50 gsm, and a DOP filtration efficiency inthe range of about 20% to 99.999%. It should be understood, however,that the ranges described herein are exemplary and that certainembodiments may include values that fall outside of these ranges.

Membrane Layer

In some embodiments, the filter media 10 may include at least onemembrane layer that is formed in a waved configuration. In theseembodiments, the membrane layer(s) may function as the filtration layer.Similarly to that described above for the fine fiber filtration layer,the membrane layer may be incorporated into the filter media betweencoarse support layers. It should be understood that though thedescription herein generally focuses on filter media that include a finefiber filtration layer, the description also applies to filter mediathat include a membrane filtration layer. For example, in the embodimentshown in FIG. 1A, the filtration layer 12 may be a membrane filtrationlayer rather than a fine fiber filtration layer as described above.

In some embodiments, filter media that include a filtration membranelayer in a waved configuration may not include any fine fiber filtrationlayers in a waved configuration. In some embodiments, one or moremembrane layers may be incorporated in a filter media in a wavedconfiguration along with one or more fine fiber layers. For example, amembrane layer may be layered on or together with a fine fiber layer. Itshould be understood that the filter media may include any number ofadditional filtration layers (which may be either membrane or finefiber) disposed between the downstream coarse support layer and theupstream coarse support layer.

In general, any suitable material may be used to form the membranelayer. Suitable materials include polytetrafluoroethylene (PTFE) (e.g.,expanded or unexpanded), polyethylene (e.g., linear low density, ultrahigh molecular weight), polypropylene, polycarbonate, polyester,nitrocellulose-mixed esters, polyethersulfone, cellulose acetate,polyimide, cellulose acetate, polyvinylidene fluoride,polyacrylonitrile, polysulfone, polyethersulfone, and polyamide, amongstothers. In some embodiments, PTFE membranes may be preferred.

The membrane layer may be a single layer film or a multilayer film. Inembodiments which use multilayer films, the different layers may havedifferent compositions. In general, the membrane layer may be formed bysuitable methods that are known in the art.

The membrane layer has a plurality of pores. The pores permit the fluidto pass through while contamination particles are captured on themembrane.

Coarse Support Layers

As also indicated above, the filter media 10 can include at least onecoarse fibrous support layer, which may optionally be charged. In anexemplary embodiment, the filter media 10 includes a downstream coarsesupport layer 14 disposed on the air outflow side O of the fine fiberfiltration layer 12 and that is effective to hold the fine fiberfiltration layer 12 in the waved configuration. The filter media 10 canalso include an upstream coarse support layer 16 that is disposed on theair entering side I of the fine fiber filtration layer 12 opposite tothe downstream coarse support layer 14. The upstream coarse supportlayer 16 can likewise help maintain the fine fiber filtration layer 12in a waved configuration. As indicated above, a person skilled in theart will appreciate that the filter media 10 can include any number oflayers, and it need not include two coarse support layers, or a toplayer. In certain exemplary embodiments, the filter media 10 can beformed from a fine fiber filtration layer 12 and a single, adjacentcoarse support layer 14 or 16. In other embodiments, the filter mediacan include any number of additional layers arranged in variousconfigurations. The particular number and type of layers will depend onthe intended use of the filter media.

The coarse support layers 14, 16 can be formed from a variety of fiberstypes and sizes. In an exemplary embodiment, the downstream coarsesupport layer 14 is formed from fibers having an average fiber diameterthat is greater than an average fiber diameter of the fine fiberfiltration layer 12, the upstream coarse support layer 16, and the toplayer 18, if provided, and the upstream coarse support layer 16 isformed from fibers having an average fiber diameter that is less than anaverage fiber diameter of the downstream coarse support layer 14, butthat is greater than an average fiber diameter of the fine fiberfiltration layer 12 and the top layer 18. In certain exemplaryembodiments, the downstream coarse support layer 14 can be formed fromfibers having an average fiber diameter in the range of about 5 μm to 40μm, and more preferably that is in the range of about 20 μm to 30 μm orabout 10 μm to 20 μm, and the upstream coarse support layer 16 can beformed from fibers having an average fiber diameter that is in the rangeof about 10 μm to 40 μm, and more preferably that is in the range ofabout 15 μm to 20 μm or about 10 μm to 20 μm.

Various materials can also be used to form the fibers of the coarsesupport layers 14, 16, including synthetic and non-synthetic materials.In one exemplary embodiment, the coarse support layers 14, 16 are formedfrom staple fibers, and in particular from a combination of binderfibers and non-binder fibers. One suitable fiber composition is a blendof at least about 20% binder fiber and a balance of non-binder fiber. Avariety of types of binder and non-binder fibers can be used to form themedia of the present invention. The binder fibers can be formed from anymaterial that is effective to facilitate thermal bonding between thelayers, and will thus have an activation temperature that is lower thanthe melting temperature of the non-binder fibers. The binder fibers canbe monocomponent fibers or any one of a number of bicomponent binderfibers. In one embodiment, the binder fibers can be bicomponent fibers,and each component can have a different melting temperature. Forexample, the binder fibers can include a core and a sheath where theactivation temperature of the sheath is lower than the meltingtemperature of the core. This allows the sheath to melt prior to thecore, such that the sheath binds to other fibers in the layer, while thecore maintains its structural integrity. This is particularlyadvantageous in that it creates a more cohesive layer for trappingfiltrate. The core/sheath binder fibers can be concentric ornon-concentric, and exemplary core/sheath binder fibers can include thefollowing: a polyester core/copolyester sheath, a polyestercore/polyethylene sheath, a polyester core/polypropylene sheath, apolypropylene core/polyethylene sheath, a polyamide core/polyethylenesheath, and combinations thereof. Other exemplary bicomponent binderfibers can include split fiber fibers, side-by-side fibers, and/or“island in the sea” fibers. Exemplary bicomponent binder fibers caninclude Trevira Types 254, 255, and 256; Invista Cellbond® Type 255;Fiber Innovations Types 201, 202, 215, and 252; and ES FibervisionsAL-Adhesion-C ESC 806A.

The non-binder fibers can be synthetic and/or non-synthetic, and in anexemplary embodiment the non-binder fibers can be about 100 percentsynthetic. In general, synthetic fibers are preferred over non-syntheticfibers for resistance to moisture, heat, long-term aging, andmicrobiological degradation. Exemplary synthetic non-binder fibers caninclude polyesters, acrylics, polyolefins, nylons, rayons, andcombinations thereof. Alternatively, the non-binder fibers used to formthe media can include non-synthetic fibers such as glass fibers, glasswool fibers, cellulose pulp fibers, such as wood pulp fibers, andcombinations thereof. Exemplary synthetic non-binder fibers can includeTrevira Type 290 and Wellman Fortrel® Types 204, 289 and 510.

The coarse support layers 14, 16 can also be formed using varioustechniques known in the art, including meltblowing, wet laid techniques,air laid techniques, carding, electrospinning, and spunbonding. In anexemplary embodiment, however, the coarse support layers 14, 16 arecarded or airlaid webs. The resulting layers 14, 16 can also have avariety of thicknesses, air permeabilities, and basis weights dependingupon the requirements of a desired application. In one exemplaryembodiment, the downstream coarse support layer 14 and the upstreamcoarse support layer 16, as measured in a planar configuration, eachhave a thickness in the range of about 10 mil to 60 mil, an airpermeability in the range of about 300 CFM to 1000 CFM, and a basisweight in the range of about 10 gsm to 100 gsm.

Outer or Cover Layer

As previously indicated, the filter media 10 can also optionally includeone or more outer or cover layers disposed on the air entering side Iand/or the air outflow side O. FIG. 1A illustrates a top layer 18disposed on the air entering side I of the filter media 10. The toplayer 18 can function as a dust loading layer and/or it can function asan aesthetic layer. In an exemplary embodiment, the top layer 18 is aplanar layer that is mated to the filter media 10 after the fine fiberfiltration layer 12 and the coarse support layers 14, 16 are waved. Thetop layer 18 thus provides a top surface that is aesthetically pleasing.The top layer 18 can be formed from a variety of fiber types and sizes,but in an exemplary embodiment the top layer 18 is formed from fibershaving an average fiber diameter that is less than an average fiberdiameter of the upstream coarse support layer 16 disposed immediatelydownstream of the top layer 18, but that is greater than an averagefiber diameter of the fine fiber filtration layer 12. In certainexemplary embodiments, the top layer 18 is formed from fibers having anaverage fiber diameter in the range of about 5 μm to 20 μm. As a result,the top layer 18 can function as a dust holding layer without affectingthe alpha value of the filter media 10, as will be discussed in moredetail below.

As shown in FIG. 1B, the filter media 10B can alternatively or inaddition include a bottom layer 18B disposed on the air outflow side Oof the filter media 10B. The bottom layer 18B can function asstrengthening component that provides structural integrity to the filtermedia 10B to help maintain the waved configuration. The bottom layer 18Bcan also function to offer abrasion resistance. This is particularlydesirable in ASHRAE bag applications where the outermost layer issubject to abrasion during use. The bottom layer 18B can have aconfiguration similar to the top layer 18, as discussed above. In anexemplary embodiment, however, the bottom layer 18B is preferably thecoarsest layer, i.e., it is formed from fibers having an average fiberdiameter that is greater than an average fiber diameter of fibersforming all of the other layers of the filter media. One exemplarybottom layer is a spunbond layer, however various other layers can beused having various configurations.

Various materials can also be used to form the fibers of the outer orcover layer, including synthetic and non-synthetic materials. In oneexemplary embodiment, the outer or cover layer, e.g., top layer 18and/or bottom layer 18B, is formed from staple fibers, and in particularfrom a combination of binder fibers and non-binder fibers. One suitablefiber composition is a blend of at least about 20% binder fiber and abalance of non-binder fiber. A variety of types of binder and non-binderfibers can be used to form the media of the present invention, includingthose previously discussed above with respect to the coarse supportlayers 14, 16.

The outer or cover layer, e.g., top layer 18 and/or any bottom layer,can also be formed using various techniques known in the art, includingmeltblowing, wet laid techniques, air laid techniques, carding,electrospinning, and spunbonding. In an exemplary embodiment, however,the top layer 18 is an airlaid layer and the bottom layer 18B is aspunbond layer. The resulting layer can also have a variety ofthicknesses, air permeabilities, and basis weights depending upon therequirements of a desired application. In one exemplary embodiment, theouter or cover layer, as measured in a planar configuration, has athickness in the range of about 2 mil to 50 mil, an air permeability inthe range of about 100 CFM to 1200 CFM, and a basis weight in the rangeof about 10 gsm to 50 gsm.

A person skilled in the art will appreciate that, while FIG. 1Aillustrates a four layer filter media, the media can include any numberof layers in various configurations. Various layers can be added toenhance filtration, to provide support, to alter structure, or forvarious other purposes. By way of non-limiting example, the filter mediacan include various spunbond wetlaid cellulose, drylaid syntheticnonwoven, wetlaid synthetic, and wetlaid microglass layers.

Method of Manufacturing

Some or all of the layers can be formed into a waved configuration usingvarious manufacturing techniques, but in an exemplary embodiment thefiltration layer 12 (e.g., fine fiber, membrane), any additionalfiltration layers, and preferably at least one of the coarse supportlayers 14, 16, are positioned adjacent to one another in a desiredarrangement from air entering side to air outflow side, and the combinedlayers are conveyed between first and second moving surfaces that aretraveling at different speeds, such as with the second surface travelingat a speed that is slower than the speed of the first surface. A suctionforce, such as a vacuum force, can be used to pull the layers toward thefirst moving surface, and then toward the second moving surface as thelayers travel from the first to the second moving surfaces. The speeddifference causes the layers to form z-direction waves as they pass ontothe second moving surface, thus forming peaks and troughs in the layers.The speed of each surface can be altered to obtain the desired number ofwaves per inch. The distance between the surfaces can also be altered todetermine the amplitude of the peaks and troughs, and in an exemplaryembodiment the distance is adjusted between 0.025″ to 4″. For example,the amplitude of the peaks and waves may be between about 0.1″ to 4.0″,e.g., between about 0.1″ to 1.0″, between about 0.1″ to 2.0″, or betweenabout 3.0″ to 4.0″. For certain applications, the amplitude of the peaksand waves may be between about 0.1″ and 1.0″, between about 0.1″ and0.5″, or between about 0.1″ and 0.3″. The properties of the differentlayers can also be altered to obtain a desired filter mediaconfiguration. In an exemplary embodiment the filter media has about 2to 6 waves per inch, with a height (overall thickness) in the range ofabout 0.025″ to 2″, however this can vary significantly depending on theintended application. For instance, in other embodiments, the filtermedia may have about 2 to 4 waves per inch, e.g., about 3 waves perinch. The overall thickness of the media may be between about 0.025″ to4.0″, e.g., between about 0.1″ to 1.0″, between about 0.1″ to 2.0″ orbetween about 3.0″ to 4.0″. For certain applications, the overallthickness of the media may be between about 0.1″ and 0.5″, or betweenabout 0.1″ and 0.3″. As shown in FIG. 1A, a single wave W extends fromthe middle of one peak to the middle of an adjacent peak.

In the embodiment shown in FIG. 1A, when the fine fiber filtration layer12 and the coarse support layers 14, 16 are waved, the resulting finefiber filtration layer 12 will have a plurality of peaks P and troughs Ton each surface (i.e., air entering side I and air outflow side O)thereof, as shown in FIG. 1C. The coarse support layers 14, 16 willextend across the peaks P and into the troughs T so that the coarsesupport layers 14, 16 also have waved configurations. A person skilledin the art will appreciate that a peak P on the air entering side I ofthe fine fiber filtration layer 12 will have a corresponding trough T onthe air outflow side O. Thus, the downstream coarse support layer 14will extend into a trough T, and exactly opposite that same trough T isa peak P, across which the upstream coarse support layer 16 will extend.Since the downstream coarse support layer 14 extends into the troughs Ton the air outflow side O of the fine fiber filtration layer 12, thedownstream coarse layer 14 will maintain adjacent peaks P on the airoutflow side O at a distance apart from one another and will maintainadjacent troughs T on the air outflow side O at a distance apart fromone another. The upstream coarse support layer 16, if provided, canlikewise maintain adjacent peaks P on the air entering side I of thefine fiber filtration layer 12 at a distance apart from one another andcan maintain adjacent troughs T on the air entry side I of the finefiber filtration layer 12 at a distance apart from one another. As aresult, the fine fiber filtration layer 12 has a surface area that issignificantly increased, as compared to a surface area of the fine fiberfiltration layer in the planar configuration. In certain exemplaryembodiments, the surface area in the waved configuration is increased byat least about 50%, and in some instances as much as 120%, as comparedto the surface area of the same layer in a planar configuration. Theincreased surface area leads to an increased filtration efficiency, aswill be discussed in more detail below.

In embodiments in which the upstream and/or downstream coarse supportlayers hold the fine fiber filtration layer in a waved configuration, itmay be desirable to reduce the amount of free volume (e.g., volume thatis unoccupied by any fibers) in the troughs. That is, a relatively highpercentage of the volume in the troughs may be occupied by the coarsesupport layer(s) to give the fine fiber layer structural support. Forexample, at least 95% or substantially all of the available volume inthe troughs may be filled with the coarse support layer and the coursesupport layer may have a solidity ranging between about 1% to 90%,between about 1% to 50%, between about 10% to 50%, or between about 20%to 50%. Additionally, as shown in the exemplary embodiments of FIG. 1A,the extension of the coarse support layer(s) across the peaks and intothe troughs may be such that the surface area of the coarse supportlayer in contact with a top layer 18A is similar across the peaks as itis across the troughs. Similarly, the surface area of the coarse supportlayer in contact with a bottom layer 18B (FIG. 1B) may be similar acrossthe peaks as it is across the troughs. For example, the surface area ofthe coarse support layer in contact with a top or bottom layer across apeak may differ from the surface area of the coarse support layer incontact with the top or bottom layer across a trough by less than about70%, less than about 50%, less than about 30%, less than about 20%, lessthan about 10%, or less than about 5%.

In certain exemplary embodiments, the downstream and/or upstream coarsesupport layers 14, 16 can have a fiber density that is greater at thepeaks than it is in the troughs, and a fiber mass that is less at thepeaks than it is in the troughs. This can result from the coarseness ofthe downstream and/or upstream coarse support layers 14, 16 relative tothe fine fiber filtration layer 12. In particular, as the layers arepassed from the first moving surface to the second moving surface, therelatively fine nature of the fine fiber filtration layer 12 will allowthe downstream and/or upstream coarse support layers 14, 16 to conformaround the waves formed in the fine fiber filtration layer 12. As thecoarse support layers 14, 16 extend across a peak P, the distancetraveled will be less than the distance that each layer 14, 16 travelsto fill a trough. As a result, the coarse support layers 14, 16 willcompact at the peaks, thus having an increased fiber density at thepeaks as compared to the troughs, through which the layers will travelto form a loop-shaped configuration.

Once the layers are formed into a waved configuration, the waved shapecan be maintained by activating the binder fibers to effect bonding ofthe fibers. A variety of techniques can be used to activate the binderfibers. For example, if bicomponent binder fibers having a core andsheath are used, the binder fibers can be activated upon the applicationof heat. If monocomponent binder fibers are used, the binder fibers canbe activated upon the application of heat, steam and/or some other formof warm moisture. A top layer 18 (FIG. 1A) and/or bottom layer 18B (FIG.1B) can also be positioned on top of the upstream coarse support layer16 (FIG. 1A) or on the bottom of the downstream coarse support layer 14B(FIG. 1B), respectively, and mated, such as by bonding, to the upstreamcoarse support layer 16 or downstream coarse support layer 14Bsimultaneously or subsequently. A person skilled in the art will alsoappreciate that the layers can optionally be mated to one another usingvarious techniques other than using binder fibers. Other suitable matingtechniques include adhesives, needling, hydroentanglement, and chemicalbinders. The layers can also be individually bonded layers, and/or theycan be mated, including bonded, to one another prior to being waved.

A saturant can also optionally be applied to the material prior todrying the material. A variety of saturants can be used with the mediaof the present invention to facilitate the forming of the layers at atemperature that is less than the melting temperature of the fibers.Exemplary saturants can include phenolic resins, melamine resins, urearesins, epoxy resins, polyacrylate esters, polystyrene/acrylates,polyvinyl chlorides, polyethylene/vinyl chlorides, polyvinyl acetates,polyvinyl alcohols, and combinations and copolymers thereof that arepresent in an aqueous or organic solvent.

In other embodiments, the resulting media can also have a gradient in atleast one, and optionally all, of the following properties: binder andnon-binder fibers composition, fiber diameter, solidity, basis weight,and saturant content. For example, in one embodiment, the media can havea lightweight, lofty, coarse-fibered, lightly bonded and lightlysaturated sheet upstream, and a heavier, denser, fine-fibered, heavilybonded and heavily saturated sheet downstream. This allows the coarserparticles to be trapped in the upstream layer, preventing earlysaturation of the bottom layer. In other embodiments, the upstream-mostlayer can be lighter and/or loftier than the downstream-most layer. Thatis, the upstream layer can have a solidity (e.g., the solid volumefraction of fibers in the web) and a basis weight that is less than thatof the downstream layer. Additionally, in embodiments where the filtermedia includes a saturant, the media can have a gradient with respect tothe amount of saturant in the upstream-most and downstream-most layers.One skilled in the art will appreciate the variety of properties thatthe layers of the media can have.

An electrostatic charge can also optionally be imparted to the filtermedia, or to various layers of the media, to form an electret fiber web.For example, a charge may be imparted to a fine fiber filtration layerprior to joining with one or more coarse support layers. In anotherembodiment, a charge is imparted to a filter media including more thanone layer, e.g., a fine fiber filtration layer and one or more coarsesupport layers. Depending on the materials used to form each of thelayers, the amount of charge, and the method of charging, the charge mayeither remain in one or more of the layers or dissipate after a shortperiod of time (e.g., within hours). A variety of techniques are wellknown to impart a permanent dipole to the polymer web in order to formelectret filter media. Charging can be effected through the use of ACand/or DC corona discharge units and combinations thereof. Theparticular characteristics of the discharge are determined by the shapeof the electrodes, the polarity, the size of the gap, and the gas or gasmixture. Charging can also be accomplished using other techniques,including friction-based charging techniques.

The filter media can also be pleated after it is formed into the wavedconfiguration, and various exemplary configurations will be discussed inmore detail below. A person skilled in the art will appreciate thatvirtually any pleating technique known in the art can be used to pleatthe waved filter media. Typically, a filter media is pleated by forminga plurality of parallel score lines in the media and forming folds ateach score line.

Filter Media Properties

As indicated above, the properties of the resulting filter media canvary depending on the configuration of the media and the intended use.In an exemplary embodiment, the waved configuration is effective toincrease the surface area of the media 10, which in turn results in themedia having improved filtration properties than an otherwise similarmedia that has a planar configuration. Furthermore, charging of thewaved media may improve certain filtration properties compared touncharged waved media in certain embodiments.

While filter performance can be evaluated based on different criteria,it is desirable that filters, or filter media, be characterized by lowpenetration across the filter of contaminants to be filtered. At thesame time, however, there should exist a relatively low pressure drop,or resistance, across the filter. Penetration, often expressed as apercentage, is defined as follows:

Pen=C/C ₀

where C is the particle concentration after passage through the filterand C₀ is the particle concentration before passage through the filter.Filter efficiency is defined as

100−% Penetration.

Because it is desirable for effective filters to maintain values as lowas possible for both penetration and pressure drop across the filter,filters are rated according to a value termed alpha (α), which is theslope of log penetration versus pressure drop across the filter. Steeperslopes, or higher alpha values, are indicative of better filterperformance. Alpha is expressed according to the following formula

α=−100 log(C/C ₀)/DP,

where DP is the pressure drop across the filter media.

In many filtering situations it is important to have a high initialalpha value. However, it is equally, if not more important, to maintainacceptable alpha values well into the filtration process. For example,in respiratory applications, manufacturing standards mandate that thefinal respiratory filter, such as a respiratory mask, be subjected toelevated temperatures to simulate an aged effect. Accordingly, thefilter media must be capable of maintaining a high alpha value whensubjected to heat.

In certain applications, such as HVAC, discharged performance is alsoimportant. Synthetic filter media are often charged in order to enhancethe filtration performance. Due to concerns that this charge willdissipate during the use of the filter, there is a movement to informusers of a filter's worst possible efficiency. EN779:2002, the Europeanstandard for coarse and fine filters, contains a mandatory test on flatpiece media before and after discharging to determine whether there is apotential for performance degradation. The test method can be used withany procedure that results in a completely discharge media. Proceduressuggested include immersion in isopropanol or surfactants in water orexposure to diesel fumes. Treatment with isopropanol is performed byfirst measuring the efficiency of untreated media samples. Next, thesamples are immersed in a 100% solution of isopropanol, and after thefilter samples have been wetted by isopropanol they are placed on aflat, inert surface in a fume cupboard for drying. After a drying periodof 24 hours, the efficiency measurements are repeated.

The DOP (dioctyl phthalate) challenge employs an automated filtertesting unit (8130) purchased from TSI, Inc. equipped with an oilgenerator. The instrument measures pressure drop across filter media andthe resultant penetration value on an instantaneous or “loading” basisat a flow rate less than or equal to 115 liters per minute.Instantaneous readings are defined as 1 pressure drop/penetrationmeasurement. According to TSI specifications, the oil generator producesa 0.33 micron mass mean diameter 0.20 micron count mean diameter withDOP, DEHS paraffin, or Emory 3004. All references herein to DOP alpharefer to a DOP challenge applied to a sample size of 100 cm². The airflow rate was 32 lpm to produce a 10.5 fpm face velocity or 76 lpm toproduce a 25 fpm face velocity.

Another exemplary test is the NaCl (sodium chloride) challenge, whichemploys an 8130 CertiTest™ automated filter testing unit from TSI, Inc.equipped with a sodium chloride generator. The average particle sizecreated by the salt particle generator is 0.26 micron mass mean diameteror 0.07 micron count mean diameter. The instrument measures a pressuredrop across the filter media and the resultant penetration value on aninstantaneous basis at a flow rate less than or equal to 115 liters perminute (lpm). The 8130 can be run in a continuous mode with one pressuredrop/penetration reading approximately every minute. All referencesherein to NaCl alpha refer to a continuous loading of NaCl particles, torepresent fine particle loading of a filter, onto a 100 cm² sample at aflow rate of 76 lpm (face velocity of 25 fpm). The sample was loaded fora period of 60 minutes at a concentration of 15 mg NaCl/m³ air for aloading of approximately 60 mg NaCl per 100 cm² sample.

Glass media which meets EN779 classification of F5 to F8 is found tohave an alpha value in the range of about 12 to 16 with DOP or DEHS(dioctyl sebacate, an accepted equivalent to DOP) when tested at a facevelocity of 5.3 cm/s before and after discharging using isopropylalcohol, as explained above. Certain media of the present inventionachieve a minimum DOP alpha of 9, and more preferably greater than about11, and most preferably greater than 16, after discharging usingisopropyl alcohol, thus providing a suitable alternative to glass media.For a DOP alpha of 9, the equivalent NaCl alpha after IPA soak is about12, for a DOP alpha of 11, the equivalent NaCl alpha after IPA soak isabout 14, and for a DOP alpha of 16 the equivalent NaCl alpha after IPAsoak is about 20. However, the alpha value of the filter media inaccordance with the present invention may vary depending on theparticular configuration of the filter media, or the filter elementcontaining the filter media.

As described herein, certain filter media may include a fine fiberfiltration layer, and optionally one or more coarse support layers,having a plurality of peaks and troughs in a waved configuration. Thefine fiber filtration layer, and optionally the one or more coarsesupport layers, may be charged. In some embodiments, such filter mediahave high DOP alpha values. For instance, a filter media may have aninitial DOP alpha value of greater than about 35, greater than about 40,greater than about 45, greater than about 50, or even greater than about60, indicating that the media has a low initial pressure drop and a highinitial efficiency. After 60 minutes of DOP loading, a filter media mayhave a DOP alpha value of greater than about 7, greater than about 9,greater than about 11, greater than about 13, or even greater than about15, indicating that the media is able to maintain acceptable alphavalues well into the filtration process even when it is charged. Theinitial pressure drop of the filter media may be, for example, less thanabout 3.0 mm H₂O, less than about 2.5 mm H₂O, or less than about 2.0 mmH₂O. The pressure drop after 60 minutes of DOP loading may be, forexample, less than about 10.0 mm H₂O, less than about 8.0 mm H₂O, lessthan about 6.0 mm H₂O, less than about 4.0 mm H₂O, less than about 3.5mm H₂O, less than about 3.0 mm H₂O, less than about 2.5 mm H₂O, or lessthan about 2.0 mm H₂O.

The filter media may have a low initial DOP penetration and a low DOPpenetration after 60 minutes of DOP loading, indicating that the filtermedia has high efficiency. For example, the initial DOP penetration maybe less than about 40%, less than about 30%, less than about 25%, lessthan about 20%, less than about 15%, or less than about 10%. In someembodiments, such as in certain paint spray and residential (e.g.,furnace) filter applications, the initial DOP penetration is less thanabout 90%, less than about 75%, or less than about 60%. The DOPpenetration after 60 minutes of DOP loading may be, for example, lessthan about 70%, less than about 60%, less than about 55%, less thanabout 50%, less than about 45%, or less than about 40%. Low values ofpenetration may be achieved in conjunction with low pressure drop valuesacross the filter, such as the pressure drop values described above. Inone set of embodiments, such as in certain paint spray and residential(e.g., furnace) filter applications, the DOP penetration after 60minutes of DOP loading is less than about 95%, less than about 85%, orless than about 75%.

A filter media including a waved and charged layer may also have a highNaCl alpha value. For instance, a filter media may have an initial NaClalpha of greater than about 40, greater than about 50, greater thanabout 55, greater than about 60, greater than about 65, or even greaterthan about 70. After 60 minutes of NaCl loading, a filter media may havea NaCl alpha value of greater than about 20, greater than about 30,greater than about 35, greater than about 40, or even greater than about45, indicating that the media is able to maintain acceptable alphavalues well into the filtration process even when it is charged. Theinitial pressure drop of the filter media may be, for example, less thanabout 5.0 mm H₂O, less than about 4.5 mm H₂O, less than about 4.0 mmH₂O, less than about 3.5 mm H₂O, or less than about 3.0 mm H₂O. Thepressure drop after 60 minutes of NaCl loading may be, for example, lessthan about 30 mm H₂O, less than about 25 mm H₂O, less than about 20 mmH₂O, less than about 15 mm H₂O, less than about 10 mm H₂O, less thanabout 7 mm H₂O, or less than about 5 mm H₂O, indicating that thepressure drop across the media is gradual over time.

The filter media may have a low initial NaCl penetration and a low NaClpenetration after 60 minutes of NaCl loading, indicating that the filtermedia has high efficiency for excluding particles. For example, theinitial NaCl penetration may be less than about 20%, less than about15%, less than about 10%, or less than about 5%. In some embodiments,such as in certain paint spray and residential (e.g., furnace) filterapplications, the initial NaCl penetration is less than about 80%, lessthan about 60%, or less than about 40%. The NaCl penetration after 60minutes of NaCl loading may be, for example, less than about 10%, lessthan about 7%, less than about 5%, less than about 3%, or less thanabout 2%. Low values of penetration may be achieved in conjunction withlow pressure drop values across the filter, such as the pressure dropvalues described above. In one set of embodiments, such as in certainpaint spray and residential (e.g., furnace) filter applications, theNaCl penetration after 60 minutes of NaCl loading is less than about65%, less than about 50%, or less than about 30%.

In some embodiments, filter media formed with a membrane layer in awaved configuration may exhibit advantageously high DOP alpha values.The filter media formed with a membrane layer in a waved configurationmay exhibit advantageously high DOP alpha values when the membrane layeris not charged and functions as a mechanical filter. For example, insome embodiments, the DOP alpha values may be greater than about 20(e.g., between about 20 and about 80, between about 20 and about 70,between about 20 and about 60, between about 20 and about 50); in someembodiments, the DOP alpha values may be greater than about 25 (e.g.,between about 25 and about 80, between about 25 and about 70, betweenabout 25 and about 60, between about 25 and about 50); in someembodiments, the DOP alpha values may be greater than 30 (e.g., betweenabout 30 and about 80, between about 30 and about 70, between about 30and about 60, between about 30 and about 50); in some embodiments, theDOP alpha may be greater than about 35 (e.g., between about 35 and about80, between about 35 and about 70, between about 35 and about 60,between about 35 and about 50); in some embodiments, the DOP alpha maybe greater than about 50 (e.g., between about 50 and about 80, betweenabout 60 and about 80, between about 70 and about 80); in someembodiments, the DOP alpha may be greater than about 60 (e.g., betweenabout 60 and about 80, between about 70 and about 80); in someembodiments, the DOP alpha may be greater than about 70 (e.g., betweenabout 70 and about 80); and in some embodiments, the DOP alpha may begreater than about 80.

MERV (Minimum Efficiency Reporting Value) ratings are used by the HVAC(Heating, Ventilating and Air Conditioning) industry to describe afilter's ability to remove particulates from the air. The MERV rating isderived from the efficiency of the filter versus particles in varioussize ranges, and is calculated according to methods detailed in ASHRAE52.2. A higher MERV rating means better filtration and greaterperformance. In an exemplary embodiment, filter media according to thepresent invention have a MERV rating that is in the range of about 7 to20, however the rating can vary based on the intended use. For example,a filter media may have a MERV rating of greater than about 13, greaterthan about 15, greater than about 17, or greater than about 19. In oneparticular set of embodiments, a charged media described herein has aMERV rating of at least 2 greater or at least 3 greater than a filtermedia having a similar construction but comprising an uncharged finefiber filtration layer.

The resulting media can also have a variety of thicknesses, airpermeabilities, basis weights, and dust holding capacities dependingupon the requirements of a desired application. Thickness, as referredto herein, is determined according to TAPPI T411 using an appropriatecaliper gage. Basis weight, as referred to herein, is determinedaccording to ASTM D-846. The dust holding capacity, as referred toherein, is tested based on a modification to ASHRAE 52.1 to test dustloading on flat sheet instead of bag. The pressure drop across a 1 ft²sample is measured at a face velocity of 25 fpm. ASHRAE dust asspecified in ASHRAE 52.1 is added in 1 gram increments until a pressuredrop of 1.5 inch H₂O is reached. The number of grams to get to thispressure drop is noted in gram/ft².

For example, in one embodiment, the resulting media can have a thicknesst_(m), as shown in FIG. 1A, in the range of about 1.5 mm to 100 mm(e.g., about 1.5 mm to 25 mm), an amplitude of the peaks and waves ofbetween about 0.025″ to 4″ (e.g., between about 0.1″ to 1.0″, betweenabout 0.1″ to 2.0″, or between about 3.0″ to 4.0″ in some applications,between about 0.1″ and 0.5″, or between about 0.1″ and 0.3″ in otherapplications), and an air permeability in the range of about 10 CFM to1000 CFM (e.g., between about 10 CFM to 300 CFM, or between about 600CFM to 700 CFM). The resulting media can also have a basis weight in therange of about 70 gsm to 1100 gsm (e.g., about 100 gsm to 500 gsm, about400 gsm to 700, or about 400 gsm to 1000 gsm), a dust holding capacityof at least about 8 g/ft² @ 25 FPM face velocity using ASHRAE dustloading to 1.5″ H₂O pressure drop, and/or a NaCl loading of less thanabout 50 mm H₂O after loading approximately 60 mg/100 cm² of 0.26 μmparticles at 25 FPM face velocity.

Filter Elements

As previously indicated, the filter media disclosed herein, which mayoptionally be charged, can be incorporated into a variety of filterelements for use in various applications, including both liquid and airfiltration applications. Exemplary uses include ASHRAE bag filters,pleatable HVAC filters, liquid bag filter media, dust bag house filters,residential furnace filters, paint spray booth filters, face masks(e.g., surgical face masks and industrial face masks), cabin airfilters, commercial ASHRAE filters, respirator filters, automotive airintake filters, automotive fuel filters, automotive lube filters, roomair cleaner filters and vacuum cleaner exhaust filters. The filterelements can have various configurations, and certain exemplary filterelement configurations are discussed in more detail below. Otherexemplary filter elements include, by way of non-limiting example,radial filter elements that include cylindrical filter media disposedtherein, micron-rater vessel bag filters (also referred to as sockfilters) for liquid filtration, face masks, etc.

Panel Filter

In one exemplary embodiment, the optionally charged filter media can beused in a panel filter. In particular, the filter media 10 can include ahousing disposed therearound. The housing can have variousconfigurations, and the particular configuration can vary based on theintended application. In one embodiment, as shown in FIG. 2A, thehousing is in the form of a frame 20 that is disposed around theperimeter of the filter media 10. In the illustrated embodiment, theframe 20 has a generally rectangular configuration such that itsurrounds all four sides of a generally rectangular filter media 10,however the particular shape can vary. The frame 20 can be formed fromvarious materials, including cardboard, metal, polymers, etc. In certainexemplary embodiments, the frame 20 can have a thickness t that is about12″ or less, and more preferably about 2″ or less. FIG. 2B illustrates aside cross-sectional view of the frame showing the waved filter media 10disposed therein. In another embodiment, the frame can be formed fromthe edges of the filter media. In particular, as shown in FIG. 3, aperimeter of the filter media 10′ can be thermally sealed to form aframe 20′ therearound. The panel filter can also include a variety ofother features known in the art, such as stabilizing features forstabilizing the filter media relative to the frame, spacers, etc.

In use, the panel filter element can be used in a variety ofapplications, including commercial and residential HVAC (e.g., furnacefilters); automotive passenger cabin air; automotive air intake; andpaint spray booth filters. The particular properties of the filterelement can vary based on the intended use, but in certain exemplaryembodiments, the filter element has a MERV rating in the range of 7 to20, and may be, for example, greater than about 13, greater than about15, greater than about 17, or greater than about 19. The filter elementmay have a pressure drop in the range of about 0.1″ to 5″ H₂O, e.g.,between about 0.1″ to 1″ H₂O.

Pleated Filter

The optionally charged waved filter media can also be pleated and usedin a pleated filter. As previously discussed, the waved media, orvarious layers thereof, can be pleated by forming score lines at apredetermined distance apart from one another, and folding the media. Aperson skilled in the art will appreciate, however, that other pleatingtechniques can be used. Once the media is pleated, the media can beincorporated into a housing, similar to the panel filter of FIG. 3A.FIG. 4A illustrates one embodiment of a pleated filter media 32 that isdisposed within a frame 30. The frame can have various shapes and sizes,as previously discussed with respect to FIG. 3A. The media can have anynumber of pleats depending on the size of the frame and the intendeduse. In certain exemplary embodiment, the filter media has 1-2 pleatsper inch, and a pleat height in the range of about 0.75″ to 2″. However,some applications utilize peaks having a height up to 12″.

In order to facilitate pleating, the filter media can beself-supporting, i.e., it can have a stiffness that allows pleating. Incertain exemplary embodiments, the minimum stiffness of the filter mediais about 200 mg with Gurley Stiffness tester to enable pleating.Alternatively, or in addition, the filter media can include variousstiffening elements. By way of non-limiting example, FIGS. 4B and 4Cillustrate a waved filter media 32 a, 32 b that is pleated, and thatincludes a stabilizing strap 34 a, 34 b that is adhered to (e.g., usingan adhesive or other bonding techniques) an air outflow side of thefilter media 32 a, 32 b. The filter media 32 a, 32 b are also showndisposed within a frame 30 a, 30 b. FIG. 4B further illustrates a screenbacking 36 a disposed on the filter media 32 a to stiffen the media 32 aand help retain the pleated configuration. The screen backing 36 a canbe an expanded metal wire or an extruded plastic mesh.

In use, the optionally charged pleated waved filter element can be usedin a variety of applications, including pleatable HVAC filters,residential furnace filters, cabin air filters, commercial ASHRAEfilters, automotive air intake filters, automotive fuel filters,automotive lube filters, room air cleaner filters, and vacuum cleanerexhaust filters. The particular properties of the filter element canvary based on the intended use, but in certain exemplary embodiments,the filter element has a MERV rating in the range of 7 to 20. Forexample, the MERV rating may be greater than about 13, greater thanabout 15, greater than about 17, or greater than about 19. The filterelement may have a pressure drop in the range of about 0.1″ to 5″ H₂O,e.g., between about 0.1″ to 1″ H₂O. The filter media can also have athickness before pleating of about 0.5″ of less, and a thickness afterpleating of about 2″ or less. However, in certain application thethickness after pleating can be up to 12″.

Bag/Pocket Filter

In yet another embodiment, the optionally charged filter media can beincorporated into a bag or pocket filter for use in heating, airconditioning, ventilation, and/or refrigeration; and micron rated liquidfilter bags. The bag or pocket filter can be formed by placing twofilter media together (or folding a single filter media in half), andmating three sides (or two if folded) to one another such that only oneside remains opens, thereby forming a pocket inside the filter. As shownin FIG. 5A, multiple filter pockets 42 can be attached to a frame 44 toform a filter element 40. Each pocket 42 can be positioned such that theopen end is located in the frame, thus allowing air to flow into eachpocket 42 in the direction indicated by line A. The frame can includerectangular rings that extend into and retain each pocket. A personskilled in the art will appreciate that the frame can have virtually anyconfiguration, and various mating techniques known in the art can beused to couple the pockets to the frame. Moreover, the frame can includeany number of pockets, but bag filters typically include between 6 and10 pockets.

FIG. 5B illustrates one pocket 42 showing three edges 42 a, 42 b, 42 cbeing closed and one edge 42 d being open for receiving airflowtherethrough, as indicated by line A. As further shown in FIG. 5B, thepocket filter 42 can also include any number of spacers 43 disposedtherein and configured to retain opposed sidewalls of the filter 42 at apredetermined distance apart from one another. The spacers can bethreads or any other element extending between both sidewalls. FIG. 5Cillustrates a cross-sectional view of the pocket filter 42 of FIG. 5B,showing the spacer 43 extending between the sidewalls. The direction ofairflow is again indicated by line A. A person skilled in the art willappreciate that various features known in the art for use with bag orpocket filters can be incorporated into the filter media disclosedherein.

The particular properties of the filter element can vary based on theintended use, but in certain exemplary embodiments, the filter elementhas a MERV rating in the range of about 7 to 20, and more preferably 13to 20. For example, the MERV rating may be greater than about 13,greater than about 15, greater than about 17, or greater than about 19.The filter element may have a pressure drop in the range of about 0.1″to 5″ H₂O, e.g., between about 0.1″ to 1″ H₂O. The filter media can alsohave a thickness that is about 2″ or less, and more preferably about0.5″ or less, however the thickness can vary depending on the intendedapplication.

By way of non-limiting example, a standard 8 pocket ASHRAE bag filtertypically has a 30″ deep pocket in a 24″×24″ frame, and yields 80 sq.ft. of media. An ASHRAE bag filter having the same dimensions, bututilizing a waved filter media according to the present invention, willyield 176 sq. ft. of media.

Facemask

In yet another embodiment, the optionally charged filter media can beincorporated into a personal protective filtration device, such as afacemask, that is designed to remove contaminants from breathable air.In one embodiment, the filter media is used to form an industrialfacemask designed for use in the workplace. The facemask may include,for example, an outer structural support layer, a filtration layer, andan inner structural support layer, although any suitable combination oflayers can be used. Each of the layers may be charged or uncharged. Thestructural support layers may be nonwoven layers that are thermallymoldable under suitable conditions, e.g., at a temperature of about105-110° C. for 6-8 seconds. The filtration layers may be formed frommeltblown or fiberglass materials. In one set of embodiments, a facemaskhas a filter area of approximately 170 cm², which is standard in theUnited States, or an area of approximately 150 cm², which may bestandard in other areas of the world.

In another embodiment, an optionally charged filter media is used in asurgical facemask. A surgical facemask includes a personal protectivefiltration device typically worn by medical personnel for two primaryreasons: to prevent the transfer of germs from medical personnel topatient (and vice versa), and to protect medical personnel from thestrike of insulting bodily fluids. A surgical facemask may include, forexample, an outer structural support layer, a filtration layer, and aninner structural support layer, although any suitable combination oflayers can be used. Each of the layers may be charged or uncharged. Insome embodiments, the structural support layers are polypropylenespunbond and the filtration layers are formed from meltblown orfiberglass materials. The filter media may be folded for larger coveragearea, and may include a filter area of, for example, 200-1000 cm².

The following non-limiting examples serve to further illustrate thepresent invention:

Example 1

Comparative Sample A (Control)

Sample A is a planar filter media that is manufactured by Johns Manvilleand sold as CM285B-2, and it is an 80-85% glass mat filter media. Theproperties of the media were tested and are listed below in Table 1under Sample A.

For all samples prepared in Example 1, the DOP Penetration and DOP alphawere measured after discharging the media using isopropyl alcohol. Inparticular, the sample was placed in a container containing a 100%isopropyl alcohol solution, and allowed to soak for approximately 5seconds or until full saturation was achieved. The sample was thenremoved from the solution and allowed to drain for approximately 30seconds. The sample was then placed in a fume/vacuum hood and allowed toair dry. Drying time was greatly dependent upon the thickness of thesample, and varied from 20 minutes to 48 hours. The DOP Penetration andDOP alpha tests were then performed.

Comparative Sample B (Control)

Sample B is a planar filter media that is manufactured by Hollingsworth& Vose Company and sold as AS8020DD, and it is 80-85% synthetic filtermedia. The properties of the media were tested and are listed below inTable 1 under Sample B.

Sample C

Sample C was formed using four layers, listed in order from upstream(air entry) to downstream (air outflow): (1) a top airlaid layer, (2) anupstream airlaid coarse support layer, (3) a fine fiber meltblown layer,and (4) a downstream airlaid coarse support layer.

The top airlaid layer was formed from 50% of a 2 denier by 6 mm Type 255bicomponent fiber available from Invista, and 50% of a 0.9 denier by 6mm Type 510 polyethyleneterephthalate (PET) fiber available fromWellman. The top airlaid layer was bonded in an oven. The top airlaidlayer had a basis weight of 25 gsm, a thickness of 30 mil, and an airpermeability of 850 CFM.

The upstream airlaid coarse support layer was formed from 70% of a 2denier by 6 mm Type 255 bicomponent fiber available from Invista, 20% ofa 0.9 denier by 6 mm Type 510 PET fiber available from Wellman, and 10%of a 15 denier by 6 mm Type 341 PET fiber available from Wellman. Theupstream airlaid coarse support layer had a basis weight of 40 gsm, athickness of 40 mil, and an air permeability of 800 CFM.

The fine fiber meltblown layer was formed from a polypropylene fiberhaving an average fiber diameter of 1.4 μm. The basis weight of themeltblown layer was 20 gsm, the thickness was 7 mil, and the airpermeability was 56 CFM.

The downstream airlaid coarse support layer was formed from 50% of a 2denier by 6 mm Type 255 fiber available from Invista, and 50% of a 15denier by 6 mm Type 341 PET fiber available from Wellman. The downstreamairlaid coarse support layer had a basis weight of 40 gsm, a thicknessof 40 mil, and an air permeability of 2000 CFM.

The upstream coarse support layer, the fine fiber meltblown layer, andthe downstream coarse support layer were formed into a wavedconfiguration by placing the layers on a first moving surface travelingat a speed of about 25 m/min. The layers traveled from the first movingsurface to a second moving surface traveling at a speed of about 10m/min, and as a result 4 waves per inch were formed. The waved webs andthe top layer were then thermally bonded in an oven at 130° C. Theproperties of the resulting media were tested and are listed below inTable 1 under Sample C.

Sample D

Sample C was repeated to form Sample D, however the fine fiber meltblownlayer was formed from a polypropylene fiber having an average fiberdiameter of 0.6 μm on a 10 gsm polypropylene spunbond. The basis weightof the meltblown layer was 7 gsm. The properties of the resulting mediawere tested and are listed below in Table 1 under Sample D.

Sample E

Sample C was repeated to form Sample E. The properties of the resultingmedia were tested and are listed below in Table 1 under Sample E.

TABLE 1 Sample A Sample B Sample C Sample D Sample E Total Basis Weight(gsm) 71 125 245 245 256 Thickness (mil) 60 65 283 308 275 AirPermeability (CFM) 61 130 71 97 67 Resistance (mmH₂O) @ 2.3 1.1 2.7 1.72.5 10.5 FPM Resistance (mmH₂O) @ 25 6 5 6.7 4.4 5.6 FPM DOP Penetration(%) at 48 88 45 52 46 10.5 FPM after IPA soak DOP alpha at 10.5 FPM 13.95.0 12.8 16.7 13.5 after IPA soak Dust Holding Capacity 7.7 5.9 12.311.5 10.3 (g/ft² @ 25 FPM to 1.5″ H₂O)

As shown in Table 1, Samples C, D, and E have improved dust holdingcapacities and higher or equivalent DOP alpha after discharge usingisopropyl alcohol as compared to Samples A and B. The various propertiesof Samples A-E are compared in graphs set forth in FIGS. 6-9.

FIG. 6 illustrates the discharged DOP Penetration versus the pressuredrop. As shown, Sample B has a high initial pressure drop whichdecreases significantly as the penetration increases. Samples A, C, D,and E, on the other hand, have a low initial pressure drop thatdecreases slowly as the penetration increases. Thus, Samples C, D, and Ehave properties that are comparable to Sample A, which is a glass fibermat, and that are superior to Sample B, which is a meltblown web. FIG. 6therefore illustrates that the waved configuration of Samples C, D, andE advantageously improve the pressure drop as a function of penetration,and thus provide a suitable alternative to glass mat fiber webs.

FIG. 7 illustrates the dust holding capacity of Samples A-E. As shown,Samples A and B show a significantly lower dust holding capacity ascompared to Samples C, D, and E. Thus, the waved configuration ofSamples C, D, and E results in an improved dust holding capacity ascompared to the planar configuration of Samples A and B.

Example 2

A first planar fine fiber meltblown layer, referred to as Meltblown C,was prepared having the same configuration as the fine fiber meltblownlayer of Sample C. The basis weight of Meltblown C was 20 gsm.

A second planar fine fiber meltblown layer, referred to as Meltblown D,was prepared having the same configuration as the fine fiber meltblownlayer of Sample D. The basis weight of Meltblown D was 20 gsm.

The NaCl loading for Meltblown C and Meltblown D, as well as for SamplesC and D from Example 1 above, were tested and the NaCl Loading at 76 lpmis shown in FIG. 8. As shown, the waved filter media of Samples C and Dshow a significant improvement in NaCl loading, as the resistanceremains low over a longer period of time, as compared to Meltblown C andMeltblown D.

Example 3

Comparative Sample F

Sample F was formed using four layers, listed in order from upstream(air entry) to downstream (air outflow): (1) a top carded nonwovenlayer, (2) a fine fiber meltblown layer, and (3) a downstream cardednonwoven layer.

The top and bottom nonwoven layers were formed from 45% of a 3 denier by1.75″ Type 202 bicomponent fiber available from FIT, and 30% of a 3denier by 2″ Type N39 PET fiber available from Poole. The top and bottomnonwoven layers were each bonded in an oven. The top and bottom nonwovenlayers each had a basis weight of 160 gsm, a thickness of 155 mil, andan air permeability of 420 CFM.

The fine fiber meltblown layer was formed from a polypropylene fiberhaving an average fiber diameter of 1.1 μm. The basis weight of themeltblown layer was 35 gsm, the thickness was 11 mil, and the airpermeability was 39 CFM.

The top and bottom nonwoven layers were positioned on opposite sides ofthe fine fiber meltblown layer to form a planar filter media. Theproperties of the resulting media were tested and are listed below inTable 1 under Sample F.

Sample G

Sample G was formed using four layers, listed in order from upstream(air entry) to downstream (air outflow): (1) a top airlaid layer, (2) anupstream airlaid coarse support layer, (3) a fine fiber meltblown layer,and (4) a downstream airlaid coarse support layer.

The top airlaid layer was formed from 50% of a 2 denier by 6 mm Type 255bicomponent fiber available from Invista, and 50% of a 0.9 denier by 6mm Type 510 polyethylene terephthalate (PET) fiber available fromWellman. The top airlaid layer was bonded in an oven. The top airlaidlayer had a basis weight of 25 gsm, a thickness of 40 mil, and an airpermeability of 850 CFM.

The upstream airlaid coarse support layer was formed from 70% of a 2denier by 6 mm Type 255 bicomponent fiber available from Invista, 20% ofa 0.9 denier by 6 mm Type 510 PET fiber available from Wellman, and 10%of a 15 denier by 6 mm Type 341PET fiber available from Wellman. Theupstream airlaid coarse support layer had a basis weight of 40 gsm, athickness of 40 mil, and an air permeability of 800 CFM.

The fine fiber meltblown layer was formed to correspond to the finefiber meltblown layer of Sample F. In particular, the fine fibermeltblown layer was formed from a polypropylene fiber having an averagefiber diameter of 1.1 μm. The basis weight of the meltblown layer was 35gsm, the thickness was 11 mil, and the air permeability was 39 CFM.

The downstream airlaid coarse support layer was formed from 50% of a 2denier by 6 mm Type 255 fiber available from Invista, and 50% of a 15denier by 6 mm Type 341 PET fiber available from Wellman. The downstreamairlaid coarse support layer had a basis weight of 38 gsm, a thicknessof 40 mil, and an air permeability of 2000 CFM.

The upstream coarse support layer, the fine fiber meltblown layer, andthe downstream coarse support layer were formed into a wavedconfiguration by placing the layers on a first moving surface travelingat a speed of about 25 m/min. The layers traveled from the first movingsurface to a second moving surface traveling at a speed of about 10m/min, and as a result 4 waves per inch were formed. The waved webs andthe top layer were then thermally bonded in an oven at 140° C. Theproperties of the resulting media were tested and are listed below inTable 2 under Sample G.

TABLE 2 Sample F Sample G Total Basis Weight (gsm) 350 259 TotalThickness (mil) 330 269 Air Permeability (CFM) 34.2 38.8 Caliper (mm)6.79 4.6 Capacity (g/m²) 128.03 324.22 Test Time (minutes) 33.81 85.27Beta75 15.8 7.6

As shown in Table 2, waved Sample G has a lower Beta₇₅ than planarSample F. Beta₇₅ is determined by ISO 16889. Using a FTI MultipassFilter Test Stand available from Fluid Technologies Inc., of Stillwater,Okla., an A2 fine dust is fed at a rate of 0.3 liters per minute intoMobil MIL-H-5606 fuel for a total flow rate of 1.7 liters per minuteuntil a terminal pressure of 172 KPa above the baseline filter pressuredrop is obtained. Particle counts (particles per milliliter) at theparticle sized selected (in this case 4, 5, 7, 10, 15, 20, 25, and 30microns) upstream and downstream of the media are taken at ten pointsequally divided over the time of the test. The average of upstream anddownstream particle counts are taken at each selected particle size.From the average particle count upstream (injected −C₀) and the averageparticle count downstream (passed thru-C) the liquid filtrationefficiency test value for each particle size selected is determined bythe relationship [(100−[C/C₀])*100%]. Another expression of efficiencyis Beta Rating. Beta₇₅ is defined as the particle size where the ratioof the upstream count (C₀) to downstream count (C) equals 75 (efficiencyequals 98.67%). The lower the Beta Rating, the lower the particle sizefor an efficiency. Generally, efficiency decreases as the particle sizedecreases.

FIG. 9 illustrates the pressure of Samples F and G as a function oftime, as tested using a multi-pass test for liquid filtration per ISO16889. During such a test, a dust is dispersed in oil, and thedispersion is passed through the filter media until a given pressuredrop is reached (172 kPa in this test). It is more desirable to have thepressure increase over a longer period of time. As shown in FIG. 9,Sample G loads in 85 minutes while the comparable flat sheet of Sample Floads in 34 minutes.

Example 4

Sample H

Sample H was formed using four layers, listed in order from upstream(air entry) to downstream (air outflow): (1) an upstream carded fibercoarse support layer, (2) a fine fiber meltblown layer, (3) a downstreamcarded fiber coarse support layer, and (4) a bottom spunbond layer.

The upstream carded fiber coarse support layer was formed from 70% of a2 denier by 1.5 inch Type 256 bicomponent fiber available from Treviraand 30% of a 3 denier by 2 inch Type P320 PET fiber available fromBarnet. The upstream carded fiber coarse support layer had a basisweight of 35 gsm, a thickness of 40 mil, and an air permeability of 800CFM.

The fine fiber meltblown layer was formed from a polypropylene fiberhaving an average fiber diameter of about 0.7 μm. The basis weight ofthe meltblown layer was 15 gsm, the thickness was 5 mil, and the airpermeability was 68 CFM.

The downstream carded fiber coarse support layer was formed from 40% ofa 2 denier by 1.5 inch Type 256 fiber available from Trevira, and 60% ofa 3 denier by 2 inch Type P320 PET fiber available from Barnet. Thedownstream airlaid coarse support layer had a basis weight of 35 gsm, athickness of 40 mil, and an air permeability of 1000 CFM.

The bottom spunbond layer was a polypropylene spunbond purchased fromPolymer Group, Inc. The bottom spunbond layer had a basis weight of 15gsm, a thickness of 3 mil, and an air permeability of 1200 CFM.

The upstream coarse support layer, the fine fiber meltblown layer, andthe downstream coarse support layer were formed into a wavedconfiguration by placing the layers on a first moving surface travelingat a speed of about 10 m/min. The layers traveled from the first movingsurface to a second moving surface traveling at a speed of about 4m/min, and as a result 3 waves per inch were formed. The waved webs andthe bottom spunbond layer were then thermally bonded in an oven at 130°C. The properties of the resulting media were tested and are listedbelow in Table 3 under Sample H.

Sample I

Sample G was repeated for Sample I, however a bonded, carded fiber layerwas used in place of the bottom spunbond layer. The bottom carded fiberlayer was formed from 50% of a 2 denier by 1.5 inch Type 256 bicomponentfiber available from Trevira, and 50% of a 0.9 denier by 1.5 inch TypeP1842B polyethyleneterephthalate (PET) fiber available from Barnet. Thebottom carded fiber layer was pre-bonded in an oven at 130° C. The topairlaid layer had a basis weight of 25 gsm, a thickness of 20 mil, andan air permeability of 890 CFM. The properties of the resulting mediawere tested and are listed below in Table 3 under Sample I.

TABLE 3 Physical Property Sample G Sample I Coverstock (SB/NW) SpunbondNonwoven Basis Weight (g/m²) 206.1 228.78 Caliper (mils) 234 457.63 AirPermeability (CFM) 81 80 Initial Values: Airflow Resistance @ 32 lpm;100 cm² (mm H₂O) 2.14 2.10 Airflow Resistance @ 76 lpm; 100 cm² (mm H₂O)5.54 5.29 NaCl Penetration @ 32 lpm; 100 cm² (%) 39.7 34.7 NaClPenetration @ 76 lpm; 100 cm² (%) 45.6 42.7 NaCl Alpha @ 32 lpm; 100 cm²(mm H₂O⁻¹) 18.8 21.9 NaCl Alpha @ 76 lpm; 100 cm² (mm H₂O⁻¹) 6.2 7.0 DOPPenetration @ 32 lpm; 100 cm² (%) 47.8 44.1 DOP Penetration @ 76 lpm;100 cm² (%) 52.4 48.7 DOP Alpha @ 32 lpm; 100 cm² (mm H₂O⁻¹) 15.0 16.9DOP Alpha @ 76 lpm; 100 cm² (mm H₂O⁻¹) 5.1 5.9 After IPA Discharge:Airflow Resistance @ 32 lpm; 100 cm² (mm H₂O) 2.12 2.03 AirflowResistance @ 76 lpm; 100 cm² (mm H₂O) 5.32 5.41 NaCl Penetration @ 32lpm; 100 cm² (%) 39.4 34.4 NaCl Penetration @ 76 lpm; 100 cm² (%) 45.739.1 NaCl Alpha @ 32 lpm; 100 cm² (mm H₂O⁻¹) 19.1 22.8 NaCl Alpha @ 76lpm; 100 cm² (mm H₂O⁻¹) 6.4 7.5 DOP Penetration @ 32 lpm; 100 cm² (%)47.5 42.6 DOP Penetration @ 76 lpm; 100 cm² (%) 52.7 47.7 DOP Alpha @ 32lpm; 100 cm² (mm H₂O⁻¹) 15.2 18.3 DOP Alpha @ 76 lpm; 100 cm² (mm H₂O⁻¹)5.2 6.0 Dust Holding Value (25 fpm to 1.5″ H2O) (grams/ 10.3 11.0 ft²)

Example 5

Sample J

Sample G was repeated for Sample J, however the fine fiber meltblownlayer was a 6 gsm, 0.7 μm polypropylene meltblown. The fine fibermeltblown layer had a thickness of 2.4 mil and an air permeability of167 CFM. The properties of the resulting media were tested and arelisted below in Table 4 under Sample J.

Sample K

Sample G was repeated for Sample K however the fine fiber meltblownlayer was a 22 gsm, 0.7 μm polypropylene meltblown. The fine fibermeltblown layer had a thickness of 6.8 mil and an air permeability of 37CFM. The properties of the resulting media were tested and are listedbelow in Table 4 under Sample K.

TABLE 4 Physical Property Sample G Sample I Coverstock (SB/NW) SpunbondSpunbond Basis Weight (g/m²) 192.4 206.1 Caliper (mils) 215 224 AirPermeability (CFM) 110 48 Initial Values: Airflow Resistance @ 32 lpm;100 cm² (mm H₂O) 1.36 3.23 Airflow Resistance @ 76 lpm; 100 cm² (mm H₂O)3.64 8.12 NaCl Penetration @ 32 lpm; 100 cm² (%) 58.8 27.6 NaClPenetration @ 76 lpm; 100 cm² (%) 63.8 34.8 NaCl Alpha @ 32 lpm; 100 cm²(mm H₂O⁻¹) 17.0 17.3 NaCl Alpha @ 76 lpm; 100 cm² (mm H₂O⁻¹) 5.4 5.6 DOPPenetration @ 32 lpm; 100 cm² (%) 65.9 33.8 DOP Penetration @ 76 lpm;100 cm² (%) 71.2 40.5 DOP Alpha @ 32 lpm; 100 cm² (mm H₂O⁻¹) 13.3 14.6DOP Alpha @ 76 lpm; 100 cm² (mm H₂O⁻¹) 4.1 4.8 After IPA Discharge:Airflow Resistance @ 32 lpm; 100 cm² (mm H₂O) 1.32 3.25 AirflowResistance @ 76 lpm; 100 cm² (mm H₂O) 3.62 8.02 NaCl Penetration @ 32lpm; 100 cm² (%) 57.3 26.9 NaCl Penetration @ 76 lpm; 100 cm² (%) 62.134.8 NaCl Alpha @ 32 lpm; 100 cm² (mm H₂O⁻¹) 18.3 17.5 NaCl Alpha @ 76lpm; 100 cm² (mm H₂O⁻¹) 5.7 5.7 DOP Penetration @ 32 lpm; 100 cm² (%)65.5 35.8 DOP Penetration @ 76 lpm; 100 cm² (%) 69.8 39.5 DOP Alpha @ 32lpm; 100 cm² (mm H₂O⁻¹) 13.92 13.73 DOP Alpha @ 76 lpm; 100 cm² (mmH₂O⁻¹) 4.31 5.03 Dust Holding Value (25 fpm to 1.5″ H2O) (grams/ 11.58.9 ft²)

Example 6

Comparative Sample L

Sample L was formed using three layers, listed in order from upstream(air entry) to downstream (air outflow): (1) a top carded nonwovenlayer, (2) a fine fiber meltblown layer, and (3) a downstream cardednonwoven layer. The sample was charged and had an unwaved configuration.

The top and bottom layers were formed from three different polyesterfibers: 60% of a 4 denier by 2″ Type P1140 fiber available from Barnett,30% of a 6 denier by 1.5″ Type T295 fiber available from Kosa, and 10%of a 1.2 denier by 1.5″ Type TP1250 fiber available from Barnett. Thethree fibers had diameters of 20.3 μm, 24.8 μm and 11.1 μm,respectively. The top and bottom nonwoven layers were each bonded in anoven. The top and bottom nonwoven layers each had a basis weight of 90gsm, a thickness of 89 mil, and an air permeability of 690 CFM.

The fine fiber meltblown layer was formed from a polypropylene fiberhaving an average fiber diameter of 1.97 μm. The basis weight of themeltblown layer was 22 gsm, the thickness was 7.5 mil, and the airpermeability was 75 CFM.

The top and bottom nonwoven layers were positioned on opposite sides ofthe fine fiber meltblown layer to form the filter media. The sample wascharged by subjecting it to four DC charge pinner bars. Each bar emitteda negative charge and operated under 30 kilovolts and 5 mA. Chargingoccurred at a temperature of 90 degrees F. and at a 15% humidity level.

Comparative Sample M

Sample M was formed using a single layer of fine meltblown fiber,constructed in an unwaved configuration. The fine fiber meltblown layerwas formed from a polypropylene fiber having an average fiber diameterof 1.0 μm. The basis weight of the meltblown layer was 11.5 gsm, thethickness was 3.9 mil, and the air permeability was 77 CFM. The samplewas charged by subjecting it to four DC charge pinner bars. Each baremitted a negative charge and operated under 30 kilovolts and 5 mA.Charging occurred at a temperature of 90 degrees F. and at a 15%humidity level.

Sample N

Sample N was formed using four layers, listed in order from upstream(air entry) to downstream (air outflow): (1) an upstream carded fibercoarse support layer, (2) a fine fiber meltblown layer, (3) a downstreamcarded fiber coarse support layer, and (4) a spunbond layer. The samplewas charged. Layers (1)-(3) had a waved configuration and layer (4) hada planar configuration.

The upstream and downstream carded fiber coarse support layers each wereformed from 65% of a 2 denier by 1.5 inch Type PC68055 polyester fiberhaving an average diameter of 14.3 microns available from Consolidated,and 35% of a 3 denier by 2 inch Type P320 polyester fiber having anaverage diameter of 17.6 microns available from Nan Ya. The upstream anddownstream carded fiber coarse support layers each had a basis weight of80 gsm, a thickness of 40 mil, and an air permeability of 219 CFM.

The fine fiber meltblown layer was formed from a polypropylene fiberhaving an average fiber diameter of 1.0 μm. The basis weight of themeltblown layer was 11.5 gsm, the thickness was 3.9 mil, and the airpermeability was 77 CFM.

The upstream coarse support layer, the fine fiber meltblown layer, andthe downstream coarse support layer were formed into a wavedconfiguration by placing the layers on a first moving surface travelingat a speed of about 10 m/min. The layers traveled from the first movingsurface to a second moving surface traveling at a speed of about 4m/min, and as a result 3 waves per inch were formed. The waved webs andthe bottom spunbond layer were then thermally bonded in an oven at 141°C.

A spunbond layer was formed from a polypropylene fiber having an averagefiber diameter of about 35 μm. The basis weight of the spunbond layerwas 15.3 gsm, the thickness was 13 mil, and the air permeability was 650CFM.

After the layers were assembled, the sample was charged by subjected itto four DC charge pinner bars. Each bar emitted a negative charge andoperated under 30 kilovolts and 5 mA. Charging occurred at a temperatureof 90 degrees F. and at a 15% humidity level.

Sample O

DOP alpha tests were performed with Samples L, M and N, as illustratedin FIG. 10, which shows DOP alpha as a function of time. As shown,Sample N has an approximately 20% higher initial DOP alpha than SampleL, and greater than 100% higher initial DOP alpha than sample M.Additionally, Sample N retains a higher DOP alpha throughout theexperiment, and has double the DOP alpha value after 60 minutes comparedto Samples L and M. FIG. 10 illustrates, therefore, that the chargedwaved configuration of Sample N advantageously improves the initial DOPalpha value, as well as the DOP alpha value as a function of time,compared to the charged, unwaved configurations of Samples L and N.

The pressure drop across each of Samples L, M and N were measured as afunction of time, as shown in FIG. 11. As illustrated in FIG. 11, thepressure drop profile for Sample L was higher than Sample M, asexpected, because the additional support layers of Sample L contributedto the relative increase in pressure drop compared to the single layerof Sample M. However, the pressure drop profile for the charged wavedmedia of Sample N was similar to that of the single layer of chargedunwaved media of Sample M, indicating that the better performancecharacteristics of Sample N (e.g., a lower pressure drop profile) wasdue to the waved configuration of the sample.

DOP Penetration tests were performed with Samples L, M and N, asillustrated in FIG. 12, which shows penetration as a function of time.Sample N generally has lower penetration values and, therefore, higherefficiency, as a function of time than Samples L or M. The lowerpenetration values contribute to the higher DOP alpha values observed inthe charged waved media shown in FIG. 10. Sample N also increases inpenetration more slowly and ends with a lower penetration at 60 minutesthan Samples L or M. This shows that the efficiency in the charged wavedconfiguration of Sample N decays more slowly compared to the charged,unwaved configurations. FIG. 12 also illustrates that the charged wavedconfiguration of Sample N has less of a change in efficiency as afunction of time at a constant pressure drop. For instance, for SampleN, the penetration at time=0 is about 16% and the penetration at time=60seconds is about 59%, resulting in a change in penetration of 43%. Forsample L, the penetration at time=0 is about 8% and the penetration attime=60 seconds is about 72%, resulting in a change in penetration ofabout 64%.

To test the response of Samples L, M and N to solid particulate loading,NaCl loading tests were performed. As shown in FIG. 13, the chargedwaved filter media of Sample N showed a significant improvement in NaClloading compared to Samples L and M, as the initial NaCl alpha valuesare higher and the NaCl alpha remains higher over a longer period oftime.

The pressure drop across each of Samples L, M and N were measured as afunction of time, as shown in FIG. 14. As illustrated in FIG. 11, thepressure drop increase for the charged waved media of Sample N is muchlower than that for the charged, unwaved media of Samples L and M.Without wishing to be bound by theory, it is hypothesized that theincreased surface area of the waved layers allows more particles to beloaded up without blocking the pores of the media, contributing to thelow overall pressure drop across the media. This shows that chargedwaved media may be advantageous for applications where loading of fineparticles is important.

NaCl Penetration tests were performed with Samples L, M and N, asillustrated in FIG. 15, which shows penetration as a function of time.For all samples, penetration decreased as a function of time. It isbelieved that this occurs because the NaCl particles form a layer withinthe media that acts as a filter. However, the penetration decreases at amuch slower rate for the charged waved media of Sample N than thecharged unwaved media of sample M, showing that sample N is loading upmore slowly with NaCl particles. The penetration may be decreasing at ahigher rate for the charged, unwaved media of sample M since the NaClparticles load much faster into this sample compared to the othersamples, as illustrated by the increase in pressure drop shown in FIG.14. Because Sample N has lower penetration values, it has a higherefficiency as a function of time than Sample M. The lower penetrationvalues of Sample N contribute to the higher NaCl alpha values observedin the charged waved media shown in FIG. 13. Sample L has lowerpenetration values than Samples M and N in FIG. 15 because Sample Lstarted off with a higher pressure drop, as shown in FIG. 14.

MERV testing was performed with Sample N (waved, charged) and Sample O(waved, uncharged), which were made into 8 pocket ASHRAE bag filterswith dimensions of 24″×24″×30″ and a surface area of 80 ft². As shown inFIG. 16, the MERV testing was run with 12 different particle size rangesat a specified face velocity of 25 ft/min at 2000 CFM. As shown in FIG.16, the filtration efficiency is much higher for smaller particle sizesfor the charged media of Sample N compared to the uncharged media ofSample O. Advantageously, the higher efficiency at the same or nearlythe same pressure drop allows for higher MERV rated filters, which maybe beneficial in the HVAC market among others. The results shown in FIG.16 indicate that the MERV rating increased from MERV 13 to MERV 15 whencomparing the uncharged and charged media, respectively.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

What is claimed is:
 1. A filter media, comprising: a membrane filtrationlayer comprising a plurality of waves having peaks and troughs in awaved configuration; and a coarse support layer that holds the membranelayer in the waved configuration and maintains separation of peaks andtroughs of adjacent waves of the filtration layer.